The short answer: A probiotic is live bacteria. A prebiotic is the fibre that feeds bacteria already in your gut. You do not always need both from a supplement, because foods like roti and onions already supply prebiotic fibre. A little extra gas when you add fibre is common.
Why is everyone asking about prebiotics right now?
Gut health is having a moment again. On 9 October 2026, TODAY.com ran an expert tip from gastroenterologist Dr Trisha Pasricha on high-fibre foods for the gut [5]. Her main advice was simple. Eat more fibre, eat a wider range of plants, and go slowly [5].
At the same time, gut-health forums are full of the same two questions. Do I need a prebiotic and a probiotic? And why did my stomach feel worse in the first week?
Both are fair questions. The labels do not help. One jar says "probiotic", another says "prebiotic", and a third says "synbiotic". Let us clear it up.
What is a probiotic?
A probiotic is a live microorganism that gives you a health benefit when you take it in the right amount. That is the official definition used by the International Scientific Association for Probiotics and Prebiotics, quoted by the US National Institutes of Health (NIH) [1].
Most probiotics are bacteria. A few are yeasts [1]. You find them in some fermented foods, such as yoghurt, in foods with added cultures, and in supplements [1].
Think of probiotics as new seeds you plant in a garden. Whether they grow depends on the soil and on what you feed them.
What is a prebiotic?
A prebiotic is food for your gut bacteria. In 2017, an expert panel defined it as "a substrate that is selectively utilized by host microorganisms conferring a health benefit" [2]. In plain words, it is something the good bacteria in your gut eat, which then does you some good.
Most prebiotics are complex carbohydrates, long chains of sugars that your own body cannot digest [1]. Two common ones are inulin and FOS, short for fructo-oligosaccharides, a type of plant fibre [1]. Your gut bacteria use them as fuel [1].
Back to the garden. If probiotics are the seeds, prebiotics are the khad, the compost you mix into the soil.
What is a synbiotic?
A synbiotic is simply a product that contains both a prebiotic and a probiotic [1]. The NIH notes that commercial products with both are often sold under this name [1].
So when you see a probiotic capsule with FOS on the label, you are looking at a synbiotic. The bacteria come with a small packed lunch.
That does not automatically make it better. It just means the product gives you both parts in one place.
Are you already eating prebiotics?
Very likely, yes. A large US study used food records from more than 15,000 Americans [4]. It found their diets supplied on average about 2.6 g of inulin and 2.5 g of oligofructose a day [4].
The biggest sources were not fancy powders. Wheat supplied about 70% of it, and onions about 25% [4].
That study was in the US, and we do not have the same numbers for Indian diets. But wheat and onions are the backbone of many Indian kitchens. If your day includes rotis and a sabzi that starts with chopped pyaaz, you are already feeding your gut bacteria some prebiotic fibre.
This is why we say you do not always need a prebiotic from a jar. Food comes first.
Why do prebiotics make you gassy at first?
Here is the honest part that most labels skip. When gut bacteria eat fibre, they ferment it, a bit like curd setting overnight. Fermentation makes gas. So more fibre for your bacteria can mean more gas for you, at least for a while.
How much fibre does it take? A 1995 study gave 14 healthy volunteers different amounts of FOS [3]. The first symptom was extra gas, which showed up above 30 g of FOS a day [3]. Bloating and stomach rumbling came above 40 g a day [3]. Cramps and diarrhoea appeared only at a much higher level, 50 g a day [3].
Those are big amounts. For comparison, the US diets above supplied about 2.5 g of oligofructose a day [4]. So in that study, healthy people coped with far more FOS than a normal diet gives.
But people differ. Some of us notice changes at much smaller amounts, especially if our usual diet is low in fibre. The NIH also says probiotic side effects are usually minor and settle on their own, and gas is the typical example [1].
The fix is boring but it works for many people. Dr Pasricha says to increase fibre slowly and drink enough water [5].
Do you need a prebiotic and a probiotic together?
Not necessarily. If you eat a varied diet with whole grains, onions, garlic, dal and fruit, your gut bacteria already get plenty to eat.
A combined product makes sense if you want both parts in one simple step. It is not magic, and we have not seen strong evidence that combining them always works better than either one alone. So we do not claim that.
What matters more is the actual strain of bacteria, the amount in each dose, and whether you take it every day.
What this means if you...
...just started a probiotic with FOS and feel gassy
Mild gas in the first days is common and often settles as your gut adjusts [1]. Drink enough water and do not suddenly pile on other fibre at the same time [5]. Follow the label, and ask your doctor if it does not settle.
...eat a varied Indian diet already
You probably get a fair amount of prebiotic fibre from rotis, onions and dal. A supplement is optional, not a must. If you add one, give it a few weeks before you judge it.
...have ongoing pain, bloating or changes in your bowel habit
Do not try to fix this with jars from the chemist. See a doctor first. Ongoing gut symptoms need a proper check, not guesswork.
Where AIM stands
We make FLORA, which pairs a probiotic with a prebiotic. It uses Bacillus coagulans, a spore-forming bacterium that survives stomach acid, unlike most Lactobacillus strains. It adds FOS as the prebiotic, plus digestive enzymes, in 2 capsules a day. We do not claim FLORA fixes any gut condition. Some people notice a little extra gas in the first days, because gut bacteria ferment FOS. If that does not settle, talk to your doctor. You can read how we choose ingredients on our science page.
Frequently asked questions
What is the difference between a prebiotic and a probiotic?
A probiotic is a live microorganism, usually bacteria, that gives a health benefit when taken in the right amount. A prebiotic is the food those gut bacteria eat, usually a type of fibre such as inulin or FOS. Think of probiotics as seeds and prebiotics as the compost that helps them grow.
Do I need to take both prebiotics and probiotics?
Not always. If you eat whole grains, onions, garlic, dal and fruit, you already get prebiotic fibre from food. A product with both is called a synbiotic, and it is simply convenient. There is no strong evidence that combining them always works better than either alone, so food should come first.
Can prebiotics cause gas and bloating?
Yes, they can. Gut bacteria ferment prebiotic fibre, and fermentation makes gas. In a 1995 study of 14 healthy volunteers, extra gas appeared above 30 g of FOS a day and bloating above 40 g a day. Sensitive people may notice changes at lower amounts, so increase fibre slowly and drink water.
Which Indian foods are natural prebiotics?
In a large US study, wheat and onions supplied most of the natural inulin and oligofructose people ate. That makes everyday rotis and onion-based sabzis useful sources. Garlic, bananas, whole grains and dal also add fibre that gut bacteria can use. A varied plate is the simplest way to feed your gut.
Is curd a probiotic?
Curd contains live bacteria, and the NIH notes that probiotics are found in some fermented foods like yoghurt. But a probiotic has a strict definition, a live microorganism shown to give a health benefit in the right amount. Not every bacterium in homemade curd has been studied that way, so curd is healthy food, not a measured probiotic dose.
Are probiotic side effects common?
The NIH says probiotic side effects are usually minor and settle on their own, with gas being the typical example. If you have a serious illness or a weak immune system, talk to your doctor before you start one. If you get pain, ongoing bloating or any worrying symptom, stop and see a doctor.
Sources
- National Institutes of Health, Office of Dietary Supplements. Probiotics: Fact Sheet for Health Professionals. Updated 25 March 2025. ods.od.nih.gov
- Gibson GR, Hutkins R, Sanders ME, et al. Expert consensus document: The International Scientific Association for Probiotics and Prebiotics (ISAPP) consensus statement on the definition and scope of prebiotics. Nature Reviews Gastroenterology & Hepatology, 2017, 14(8):491-502. doi:10.1038/nrgastro.2017.75
- Briet F, Achour L, Flourié B, et al. Symptomatic response to varying levels of fructo-oligosaccharides consumed occasionally or regularly. European Journal of Clinical Nutrition, 1995, 49(7):501-507. PubMed 7588500
- Moshfegh AJ, et al. Presence of inulin and oligofructose in the diets of Americans. Journal of Nutrition, 1999, 129(7 Suppl). PubMed 10395608
- Kee C. 6 high-fiber fall foods for better gut health, recommended by a GI doctor. TODAY.com, 9 October 2026. today.com
This article is for education only and is not medical advice. Supplements are not a substitute for a varied diet or for treatment from a qualified doctor. If you are pregnant, breastfeeding, on medication, or have a medical condition, talk to your doctor before starting any supplement. Individual results vary.
Photo: Anurag Kothare via Pexels.